NASA Technical Reports Server (NTRS) 20160008018: Aluminum 2195 T8 Gore Development for Space Launch System Core and Upper Stage George C. Marshall Space Flight Center Research and Technology Report 2014

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by  NASA Technical Reports Server (NTRS)

Aluminum 2195 T8 Gore Development
for Space Launch System Core
and Upper Stage
Project Manager(s)/Lead(s)
Martin Volz/EM31
(256) 544–5078
Sponsoring Program(s)
Human Exploration and Operations Mission Directorate
Space Launch System Advanced Development
Project Description Figure 1: Gore panels are welded together to form
the dome ends of SLS cryogenic tanks.
Gores are pie-shaped panels that are welded together
to form the dome ends of rocket fuel tanks as shown in
figure 1. Replacing aluminum alloy 2219 with alumi-
num (Al)-lithium (Li) alloy 2195 as the Space Launch
System (SLS) cryogenic tank material would save enor-
mous amounts of weight. In fact, it has been calculated
that simply replacing Al 2219 gores with Al 2195 gores
on the SLS core stage domes could save ~3,800 lbm.
This is because the Al-Li 2195 alloy exhibits both higher
mechanical properties and lower density than the SLS
baseline Al 2219 alloy. Indeed, the known advantages
of Al 2195 led to its use as a replacement for Al 2219 in
the shuttle external tank program. The required thick-
Figure 2: A finite element analysis model was used to determine
nesses of Al 2195 gores for either SLS core stage tanks the magnitude and variation of strain induced during the
or upper stage tanks will depend on the specific design stretch-forming operation.
configurations. The required thicknesses or widths may
exceed the current experience base in the manufacture of results (fig. 2). One 0.525-inch-thick and two 0.75-inch-
such gores by the stretch-forming process. Accordingly, thick Al 2195 plates were successfully stretch formed
the primary objective of this project was to enhance the into gores using an existing die of the Ares I contour
formability of Al 2195 by optimizing the heat treatment (fig. 3). Use of the Ares I die was a significant cost sav-
and stretch-forming process for gore thicknesses up to ings, as an SLS die did not have to be developed and
0.75 inch, which envelop the maximum expected gore constructed. Also, the Ares I contour is more severe
thicknesses for SLS tank configurations. than the SLS contour and therefore successful stretch-
forming operations demonstrated with the Ares I die
Formability data and heat-treating parameters were can also be expected to be successful with a die of the
determined prior to stretch forming the 0.525- and SLS contour.
0.75-inch-thick plates. The data were used in the finite
element model that was developed to help guide the
stretch-forming operations and to help interpret the
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Potential Applications
The intended primary applications for this technology
development were SLS core and upper stage cryogenic
fuel tanks. This project demonstrated that relatively
thick (up to 0.75 inch) Al 2195 plates can be processed
by stretch forming. Thus, any aerospace application
S
where increased strength and weight savings are desired
L
can take advantage of this technology. S

A
D
Notable Accomplishments
Figure 3: An aluminum panel is stretch formed All of the planned tasks for this project were success-
into the desired contour using a die.
fully completed.1 An annealing treatment that led to
a higher forming range and strain hardening expo-
Mechanical testing of the 0.525- and 0.75-inch Al 2195
nent was utilized to anneal 0.525- and 0.75-inch Al
gores showed greater than expected tensile properties
2195 plates prior to gore stretch forming. One 0.525-
when compared to the Lockheed Martin Engineering
and two 0.75-inch-thick plates were successfully
Materials Specifications for Al 2195, STM 11-A1-LM,
stretch formed into gore contours and heat treated to
which was developed for the external tank program.
the T8 temper (fig. 4). Mechanical testing of the gores
The fracture toughness is also satisfactory and can be
resulted in tensile properties that exceeded the specifi-
improved further with an optimization in the aging treat-
cations for Al 2195. Finally, a detailed plan was devel-
ment parameters. The results of this study were very
oped for future work to enable the incorporation of
promising. All of the formability and mechanical test
Al 2195 gores into the SLS program.
data gained from this program indicate that the stretch-
formed 2195 gores have sufficient material properties
to replace the existing Al 2219 alloy that is the current
baseline for SLS flight domes.
Anticipated Benefits
Prior to this study, Al 2195 plates thicker than 0.325 inch
had never been stretch formed. Therefore, it was
necessary to perform formability studies on Alcoa
0.525- and 0.75-inch-thick plates to ensure that the
prescribed annealing treatment indeed improved their
formability. Tensile tests were performed for 0.525- and
0.75-inch-thick Al 2195 plates to compare the effects
of annealing treatment on the forming range and strain
hardening exponent. The annealing treatment that led to
Figure 4: The three completed gore panels after delivery to
a higher forming range and strain hardening exponents
MSFC. Test specimens were cut from the ends of two of the gore
was selected to anneal 0.525- and 0.75-inch Al 2195
panels for mechanical and fracture toughness testing.
plates prior to gore stretch forming. This annealing pro-
cess was developed at NASA Marshall Space Flight References
Center (MSFC) and is being patented (MFS-32954-1).
The NASA annealing process led to a higher strain 1. Volz, M.P.; Chen, P.S.; Gorti, S.; and Salvail, P.:
hardening exponent and higher formability, and dem- “Development of Aluminum-Lithium 2195 Gores
onstrated that large-scale rocket domes can be reliably by the Stretch Forming Process,” National Space
manufactured by the stretch-forming process with the and Missile Materials Symposium, Huntsville, AL,
lightweight Al-Li 2195 alloy. June 23–26, 2014.
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